Research On Ferroelectric Energy Storage Capacitor Based On Sterilization Application Of High-voltage Pulsed Electric Field

Saccharomyces cerevisiae is one of the main culprits of milk caking and flatulence.Conventional thermal sterilization does great damage to the nutrients of milk and consumes more energy.For yeast with intact cell structure,the non-thermal sterilization technology of high-voltage pulsed electric field sterilization has received attention.In this thesis,we use high voltage pulsed electric field sterilization technology to prevent and control yeast in milk,and study the effects of electric field strength,electrode area,and cycle number on yeast inactivation.The core component of the high-voltage pulse system is an energy storage capacitor with charge and discharge functions.In this thesis,single-phase(Bi_0.5Na_0.5)TiO₃（BNT）ceramic capacitors were modified by a combination of ion doping and component compounding methods,and performance studies and sterilization tests were conducted,mainly as follows:Firstly,(Bi_0.5-xSr_xNa_0.5)TiO₃ capacitors were prepared by doping Sr ions in the A-site of single-phase BNT ceramic capacitors.Compared with pure BNT ceramics,(Bi_0.44Sr_0.06Na_0.5)TiO₃ ceramic capacitors have a larger breakdown field strength of 160 KV/cm while retaining a maximum polarization strength of 44.17μC/cm² due to larger residual polarization,resulting in an unsatisfactory energy storage efficiency of 12.1%.The 0.9(Bi_0.44Sr_0.06Na_0.5)TiO₃-0.1CaTiO₃ composite ceramic capacitor was prepared by introducing CaTiO₃,a homologous element oxide of Sr ion,through component doping.The energy storage density is 3.52 J/cm³,the energy storage efficiency is 73.3%,the temperature is between 25-80℃,the energy storage efficiency fluctuates nearly 20%,and the temperature stability needs to be optimized.Subsequently,（1-x）(Bi_0.44Sr_0.06Na_0.5)TiO₃-xCa_0.25Sr_0.75TiO₃（BSNT-CST）composite ceramic capacitors with two identical steps of introduction of Sr ions were prepared through a combination of ion doping and component compounding,and the 2-valent Sr ions were successfully introduced into both phases to enhance the ion concentration inside the material,resulting in better consistency of grain size,uniform internal impedance,and effective enhancement of breakdown field strength.When x=0.7,the breakdown field strength reaches 420 KV/cm,the energy storage density is 4.91 J/cm³,and the energy storage efficiency is88.0%.The frequency test shows that the energy storage efficiencyηfluctuates within 6%at 10-150 Hz.In order to break the long-range order of internal electric domains of single BNT-based ceramic,a second phase base NN ceramic is introduced to compound BNT-based ceramic and NN ceramic 1:1 to refine the electric domains,disrupt the self-polarization direction,reduce the cell volume,effectively improve the breakdown electric field and reduce the residual polarization.The x/2((Bi_0.46Sr_0.06Na_0.5)TiO₃-NaNbO₃)-（1-x）Ca_0.25Sr_0.75TiO₃（BSNT-NN-CST）composite ceramic capacitors were prepared,and the study showed that the relaxation of the composite was optimal when x=0.6,and the corresponding 0.3BSNT-0.3NN-0.4CST ceramic The breakdown field strength of the capacitor is 530KV/cm,the reversible energy storage density is5.96J/cm³,and the energy storage efficiencyηis 87.5%.The frequency test and temperature stability test show that the energy storage efficiencyηfluctuates within 3%at 10-250Hz,and the good temperature stability in the range of 25-125℃,and the fluctuation of energy storage efficiency is less than 10%.Finally,comparing the energy storage performance,charging and discharging performance,frequency and temperature stability of the studied ceramic capacitors,the 0.3(Bi_0.46Sr_0.06Na_0.5)TiO₃-0.3NaNbO₃-0.4Ca_0.25Sr_0.75TiO₃ ceramic capacitor with the best overall performance was selected as the energy storage element to build a milk sterilization system for the electrical treatment of yeast in milk.treatment.It was shown that increasing the electric field strength,decreasing the electrode area and increasing the number of discharges were beneficial to increase the sterilization effect on yeast.In each experimental group,the yeast showed 98%mortality rate of adhesion in the group treated with electric field of 30KV/cm,electrode area of64mm² and 100 cycles,and the sterilization effect was obvious compared with the control group.